Given the dearth of regulatory guidance and empirical research on practices of providing payments to research participants, our study aimed to examine whether there were significant differences in payment amounts between sociobehavioral and biomedical studies and to examine study factors that may explain payment differences. This study reviewed 100 sociobehavioral and 31 biomedical protocols. Results showed that both biomedical studies and sociobehavioral studies had a wide variation of payments and, on average, the biomedical studies paid significantly more. Additionally, more biomedical studies offered payment than sociobehavioral studies. The primary factors that explained differences in payment amounts between sociobehavioral and biomedical studies were the number of study visits, study time, participation type, risk level, and research method. These findings provide pilot data to help inform future ethical decision-making and guidance regarding payment practices.